The present invention relates to a solenoid valve for controlling a fuel injector of an internal combustion engine.
A solenoid valve is described, for example, in German Patent Application No. 197 08 104. The solenoid valve may be used, for example, to control the fuel pressure in the control pressure chamber of a fuel injector, for example, an injector of a common-rail injection system. The fuel pressure in the control pressure chamber controls the movement of a valve plunger, which is used to open or close an injection orifice of the fuel injector. The solenoid valve includes an electromagnet arranged in a housing part, a movable armature, and a control valve member, which is moved with the armature. A closing spring acts upon the control valve member in the closing direction and the control valve member cooperates with a valve seat of the solenoid valve, thus controlling the fuel discharge from the control pressure chamber. It is believed that these solenoid valves are disadvantageous in that they exhibit armature bounce. When the magnet is de-energized, the closing spring of the solenoid valve accelerates the armature and the control valve member toward the valve seat to close a fuel discharge passage from the control pressure chamber. The impact of the control valve member on the valve seat may cause the control valve member to oscillate and/or bounce at the valve seat in a disadvantageous manner, thereby impairing the control of the injection process.
In the solenoid valve described, for example, in German Patent Application No. 197 08 104, the armature has a two-part design, which includes an armature pin and an armature plate slidably supported on the armature pin, so that the armature plate continues to move against the elastic force of a return spring when the valve control member hits the valve seat. Subsequently, the return spring restores the armature plate to its original position at a stop of the armature pin. Due to the two-part armature, the effective mass to be decelerated and, consequently, the bounce-causing kinetic energy of the armature striking the valve seat, may be reduced. However, the armature plate may disadvantageously oscillate on the armature pin after the closure of the solenoid valve. Since a defined injection quantity may be produced again by controlling the solenoid valve only after the armature plate has stopped oscillating, the post-oscillation of the armature plate should be reduced, for example, to obtain short intervals between, for example, a preinjection and a main injection.
To solve this problem, German Patent Application No. 197 08 104 describes an overtravel stop that limits the path length by which the armature plate may slide on the armature pin. The overtravel stop is immovably mounted in the housing of the solenoid valve between the armature plate and a slide piece, which guides the armature pin. When the armature plate approaches the overtravel stop, a hydraulic damping chamber is formed between the facing sides of the armature plate and the overtravel stop. The fuel contained in the damping chamber produces a force that counteracts the movement of the armature plate. In this manner, the post oscillation of the armature plate may be damped and the post-oscillation time of the armature plate may be shortened. However, it is believed that the required overtravel distance of the armature plate must be adjusted in the housing of the solenoid valve during the assembly of the solenoid valve. This may require a costly modification of the manufacturing process if the manufacturing facilities have to be retrofitted accordingly.
It is believed that an exemplary solenoid valve according to the present invention is advantageous in that the armature, including the armature plate, armature pin, return spring, and the overtravel stop, may be preassembled outside of the assembly line of the fuel injector, and the required sliding path of the armature plate on the armature pin may be adjusted outside of the housing of the fuel injector. Subsequently, the preassembled armature assembly may be fitted into the housing of the solenoid valve. No costly modification of the assembly line may be required. Moreover, since the return spring, which presses the armature plate against a first stop on the armature pin with a first end in its resting position, is not immovably supported with the second end in the housing of the solenoid valve, but rather is braced against a supporting piece, which is secured to and moved with the armature pin, the return spring does not counteract the closing spring of the solenoid valve acting upon the armature pin. Therefore, the closing spring of the solenoid valve may have a lower spring tension force. Since the return spring does not counteract the closing spring, the return spring does not influence the dynamic performance of the armature pin.
The armature pin may be slidably supported in an opening of a slide piece, which is immovably mounted in the housing of the solenoid valve, and for the slide piece side facing the armature plate to include a recess, in which the supporting piece is located. The supporting piece is secured to the armature pin, the outer contour of the supporting piece being spaced apart from the inner contour of the recess by a gap. In this manner, a hydraulic damping chamber may be formed through the approximation of the supporting piece to the inner wall of the recess of the slide piece and the fuel, which is compressed between the supporting piece and the recess, may damp the impact of the control valve member coupled to the armature pin.